Hydrogen Isotope Permeation Behavior Of CoCrMnFeNi And AlCoCrFeNi High Entropy Alloys Before And After Oxidation

High entropy alloys(HEAs)are a new alloy concept that has received a great deal ofattention from researchers in recent years,it leaves behind the limitations of traditional alloys with a single primary element.Because of the high entropy effect,the lattice distortion effect,the sluggish diffusion effect,and the cocktail effect,HEAs have excellent performance and are being studied as future reactor structural materials or even cladding materials in the field of nuclear energy.Certain high-entropy alloys have good mechanical properties at high temperatures,corrosion resistance and irradiation resistance.The hydrogen isotope permeation behavior of high entropy alloys should be a key concern,both as structural materials or cladding materials for pressurized water reactors,Generation IV reactors and even fusion reactors.For example,there is a large amount of lithium in the fuel salt of molten salt reactors,while lithium will produce tritium after irradiated by neutrons.The permeation of tritium through the material into the environment will cause environmental pollution.Deuterium and tritium are used as fuel in fusion reactors,so the permeation behavior should be considered.The common high-entropy alloys CoCrMnFeNi and AlCoCrFeNi are used as researchobjects in this paper,and the dynamic gas-driven permeation method is used to measure the deuterium permeability and diffusion coefficient of the two alloys at 20 kPa?100 kPa and300^°C?500^°C.The permeability pre-factor??,the permeation activation energy per molar atom Q_?>,the diffusion coefficient pre-factor Do,and the diffusion activation energy per molar atom Q are also calculated,and the changes in the samples before and after permeation wereobserved by combining SEM,XRD,EDS and EBSD.Considered the oxidation behavior ofHEAs,the permeation experiments are also done for the HEAs after oxidation at 550^°C for 24hours in air.It was found that the steady-state permeation flux of deuterium in both CoCrMnFeNi andAlCoCrFeNi is linearly dependent on P^1/2,i.e.,deuterium atom diffuses in CoCrMnFeNi with FCC structure and AlCoCrFeNi with BCC structure by body diffusion,and the body diffusionprocess is a rate-controlled step of the permeation process in the range of 20 kPa?100 kPa.ThepermeabilityofdeuteriuminCoCrMnFeNisatisfies<P=8.41 X10_ex⁴p(—^68.92:^'^m??)(_mol/(_m?₅?MP_a¹/²)^,_and th_e diff_usi_{on coe}ffi_ci_ent _sati_sf_ies D=1.00 X 10 _ex^?5p(—^6Q.67^'^m?D(_m²/_s).Whil_e th_e p_ermeability _of d_eut_eri_um in AlC_oCrF_eNi satisfies<P=1.51 x 10⁶exp(—⁵⁶¹³:J'^mQ?)?s?MPa^1,2))and the diffusion coefficient satisfies D=1.82 X 10⁶exp^43A1(m²/s).The permeability of CoCrMnFeNi is larger than that of Zr-4 alloy and 316 stainless steel,while the diffusioncoefficient of it is close to that of 316 stainless steel.The permeability of AlCoCrFeNi is close to that of 316 stainless steel,lower than that of CoCrMnFeNi,but the diffusion coefficient of it is greater than that of CoCrMnFeNi with FCC structure,indicating that deuterium is less solublein AlCoCrFeNi.However,after a long period of continuous testing,the Mn elements will accumulate atthe grain boundaries,and MnO will be produced,resulting in a slight decrease in the permeability and diffusion coefficient of the material.After oxidation at 550^°C for 24 h,an oxide film is formed on the surface of CoCrMnFeNiwith Mn2?₃ as the outer layer and Cr2?₃ as the inner layer,which reduces the permeability of the material,with a permeation reduction factor about 10.AI₂O₃ and Cr2?₃ is formed on the surface of AlCoCrFeNi after o_xidation,resulting in a lower permeability,but because AlCoCrFeNi has excellent oxidation resistance,the decrease of permeability of after oxidation is small.